Microwave heating involves multi-physical effects such as the electromagnetic，thermal, physical parameters of heating objectives varying with the temperature. The multi-physics simulation, which couples with the electromagnetic field，heat conduction and material physical parameter equations to construct a multi-physics equation，and numerically solves the equation to analyze the temperature variation in the microwave heating procedure. Taking 2.45 GHz microwave power heating water as an example，the multi-physics simulation is conducted to get the microwave power distribution，heat accumulation and temperature rise during the heating process. Moreover，an experiment equipment of microwave heating water is designed and manufactured. In the working frequency of 2.45 GHz，the testing return loss is 16.2 dB. The input power is set to 40 W and the temperature rises are tested at 4 designed points within 60 seconds of heating time. A good agreement is shown between the multi-physics simulation results and the measurement results，which validates the proposed multi-physics simulation.